End effectors, or hands, for robotic arms continue to be a limiting element for efficient use. The "fingers" are usually formed with flat gripping surfaces, or specially shaped for specific use on singular items. There are semi-universal hands with gripper mechanisms driven by pneumatics, cams, or cables, remotely controlled by computer and requiring feedback of gripping force from force/torque sensors.
One example of a universal hand is the three-finger hand disclosed in U.S. Pat. No. 4,558,911. Each finger has three joints that are driven by cable "tendons," each equipped with a cable tension sensor to prevent slack. Since each finger requires the control of several cables and use of force/torque sensing, the computerized control of the hand of the U.S. Pat. No. 4,558,911 is rather complex.
In order to grip an object, such as a ball, without crushing or damage to the ball, all cables must be simultaneously controlled for all three fingers. While the hand of the U.S. Pat. No. 4,558,911 can hold a wide variety of objects without changing grippers, the complexity of control may present some disadvantages.
It is known to employ a plurality of pistons housed in cylinders and fed by hydraulic fluid to confrom without feedback or active control, to a workpiece. In a multi-piston closed hydraulic system, loading one piston will cause a pressure to be exerted equally on all other pistons, and they will move outwards in proportion to their share of the volume displaced by the loaded piston. All unloaded pistons of the same diameters move out equal distances and exert equal forces against any encountered load.
U.S. Pat. No. 2,882,771 to Blazek discloses a workpiece holder having a plurality of fingers, or pistons, 11 and 12 extending outwardly from hydraulically-driven cylinders 9 and 10 as shown in FIGS. 4 and 5 thereof. The cylinders in Blazek U.S. Pat. No. 2,882,771 are interconnected by a common hydraulic fluid reservoir. As pressure is exerted by a workpiece on one of the fingers, that finger retracts and an outward force is thus equally applied to the other fingers as described at column 2 lines 15 through 35. A somewhat similar type of operation is disclosed in U.S. Pat. No. 4,284,267 to Marben for opposed faces of a vice. See FIG. 3 and column 4, lines 5 through 12.
Some variations of the above-described hydraulic principle are disclosed in Japanese Pat. No. 52-13275; Russian Pat. No. 889,423 and U.S. Pat. No. 3,908,318 to Wallin. The Russian patent applies the known hydraulic reservoir technique to a robot end effector.
In all of the prior art common reservoir disclosures, the pistons provide the same area to the hydraulic fluid, and thus move the same distance in response to equal hydraulic force.
The IBM Technical Disclosure Bulletin Vol. 19 No. 6 November 1976, pages 2121-2122 shows pivoting pads or chucks 12 mounted on the ends of fingers or shafts 14. See FIG. 1c and the second paragraph of page 2121. The pivot is very slight, no centering spring is taught or disclosed, and a hydraulic reservoir system is not disclosed.
An article published at page 16 in the October 1985 issue of Popular Science discloses a robot gripper, which is described as: "Two fingerlike arrays, each composed of 127 telescoping pins that can ride up or down independently." This article is not considered prior art. However even if it is prior art, the disclosure implies either the common hydraulic principle or independent spring-loaded pins.